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Developing the department of radio astronomy

RELATED STORIES

Moving to the Mullard Radio Astronomy Observatory at Lord's Bridge
Antony Hewish Astronomer
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Then the subject began to get… get expensive. You don’t call £100,000 expensive nowadays, but we had a grant from the Mullard [Radio] Company, and Ratcliffe was instrumental in… in the politics of that. And Neville Mott was then the Cavendish Professor, he’d taken over from Laurence Bragg. Laurence Bragg, a crystallographer, was very supportive of this work, but he… he didn’t really know what was going on. Ratcliffe knew what was going on and… and gave it strong support and he engineered really the grant with the Mullard Radio Company – they… they were into television then in a big way – and… we formally opened in 1957, but the observatory had been going… I made some of the very first observations actually with my solar coronal scattering work to test the site, and in 1955 I spent a lot of time myself looking around for suitable sites in East Anglia where we could actually do this work. I mean… Martin Ryle was interested in a site about a mile across, if… if you can have it, so that he could develop his interferometry on very wide baselines. And I went round looking with a… with a man from the Department of Estate Management at old airfields because you’d think the obvious place for a radio astronomy site is… is an airfield because they’re large and they’re flat and… and they’re in parts of the country which are not good agricultural… normally good agricultural regions – and East Anglia was really a huge airbase just… just after the war, because obviously bomber command was nearer Europe in East Anglia than anywhere else, and East Anglia being an open, flat… countryside was the ideal place for airbases. And I looked at… oh, I must have looked at… at more than 10 airfields within 30 miles from Cambridge. And we had, in fact, almost decided to move to a new site near Thetford which was an old army firing range, actually, and when eventually with this man from Estate Management we discovered Lord’s Bridge which was… which was an Air Ministry site, not a flying site. But it was very flat and the farmland wasn’t very good and it was being partly farmed but not… not farmed very… very productively. And it… it was up for grabs, as it were, and it was big enough for us to build our first radio telescopes and it was within cycling distance from Cambridge. I discovered that airfields were not really flat enough. You might think that airfields are the flattest place you can be, but it has runways that are flat but they are normally arranged in a triangular fashion and in between anything can go on, whereas Martin Ryle was looking for a big, flat… totally flat area, not… not just flat lines.

And so that’s how it was and we were beginning to move out to Lord’s Bridge and construct things in 1955, and the observatory was formally opened in 1957 by Edward Appleton himself. And we got on rapidly with instruments that were really doing the job and had done the job that… that Lovell was designing his dish for. And his dish only came into operation in 1957 when much of the work, for which the dish had been designed originally, had been done by Martin Ryle using his instruments here… here, at Cambridge. He was all for getting on with the job quickly, rather than trying to think of the best… perhaps the best instruments in the world and taking years and years to build it. And from then on… I mean, the development of instruments at Lord’s Bridge was… was extremely… extremely rapid. I mean, the… the 4C antenna which used a one-dimensional synthesis with a movable element which went north-south and synthesised effectively two large, about… about 400–500 km square areas, dishes, gave us high angular resolution but not… couldn’t map things. It wasn’t… it wasn’t a filled area, it was interferometer, so essentially it put… it put very accurate fringes across the sky and you could locate things and determine and know that they were small and… and they were probably radio galaxies, but you couldn’t actually map them. But his first aperture synthesis came with the… with the one mile – well, I mean, the aperture synthesis as an interferometer was… was the first instrument we built, 4C, and that was beginning to survey in 1957 when Jodrell Bank was just beginning to make its very first measurements also. But I think we were… it’s fair to say we were well ahead on the astronomical side, as… as compared to… to Jodrell Bank, because as Martin Ryle’s wisdom in… in doing these extremely effective scientific things but much more cost-effective from a… from a building point… point of view. But the mapping and knowing what radio galaxies looked like followed the early work and that came with the… the 1-mile telescope which was able to use Earth rotation synthesis. You build a railway line, as you know, and put dishes on it, because you’ve used this yourself, and in 24 hours each antenna is carried in a ring round the other one. And you can synthesise an… an area and, in that way, with a computer, synthesise the telescope which is about 1 mile in aperture as compared to the 250-foot dish that… that Lovell was able to build ultimately at… at Jodrell Bank.

And from the… that was going within a few years, the 1-mile telescope, that was in the early 1960s, and then Martin Ryle was planning an even better instrument, the 5 km, extending that to a baseline of 5 km. And that was the last instrument he built at Lord’s Bridge, that took from 1960 to 1970, more or less, to build, and that was a world… an absolute world beater. And that gave the first detailed maps of radio galaxies which was sufficiently powerful to show the mechanism that drives radio galaxies – the fact that you have a powerful energetic source in the nucleus of a galaxy which sends jets in both directions and… and those jets light up clouds of plasma at the outside. And that explains the… the characteristic shape of many of our… of our radio galaxies. But that was the… I mean, that’s… that was an extremely rapid development when you think of it in the history of radio astronomy because it… it went from the very simplest of instruments to… to a powerful synthesis telescope in… in a matter of just over 15 years or… or so. I mean, from the… from the 1950s to the mid 1960s, you know, Martin Ryle was developing the… the 4C antenna, the… the 1-mile telescope and the 5-km telescope, and they came one after the other in quick succession. And that was simply because, I think, he didn’t require international cooperation, he was a powerful enough figure to get… to get the funding. And we could get on with it with a minimum of effort here, doing most of it totally within the Cavendish infrastructure, essentially.

Born in 1924, Antony Hewish is a pioneer of radio astronomy known for his study of intergalactic weather patterns and his development of giant telescopes. He was awarded the Nobel Prize for Physics in 1974, together with fellow radio-astronomer Sir Martin Ryle, for his decisive role in the groundbreaking discovery of pulsars. He also received the Eddington Medal of the Royal Astronomical Society in 1969.

Listeners: Dave Green

Dave Green is a radio astronomer at the Cavendish Laboratory in Cambridge. As an undergraduate at Cambridge his first university physics lecture course was given by Professor Hewish. Subsequently he completed his PhD at the Cavendish Laboratory when Professor Hewish was head of the radio astronomy group, and after postdoctoral research in Canada he returned to the Cavendish, where he is now a Senior Lecturer. He is a Teaching Fellow at Churchill College. His research interests include supernova remnants and the extended remains of supernova explosions.

Duration: 8 minutes, 25 seconds

Date story recorded: August 2008

Date story went live: 25 June 2009